Heme/Copper and Heme/Nonheme Iron O(2) and NO Reactivity

描述（由申请人提供）：长期的研究目标是设计、合成和研究模型化合物系统，这些系统可以帮助阐明血红素-铜氧化酶（HCOs）、一氧化氮还原酶（NORs）和相关蛋白质利用的二氧（O2）和氮氧化物（NOx）化学的基本方面，金属连接、光谱和反应性。HCOs和NOR是进化相关的酶，在有氧和厌氧生物的细胞过程中起着关键作用。它们有一个共同的血红素/M （M = Cu或非血红素Fe）活性位点，分别还原裂解O2或NO。该研究将有助于更好地了解酶的结构和机制，为O2、NO和亚硝酸盐（NO2-）的生物处理提供全面和基础的基础，甚至超越血红素和Cu金属蛋白领域。具体目标包括：(1)血红素/Cu- O2加合物的表征，新的质子化和低自旋衍生物，并阐明它们的结构和电子/键性质；(2)血红素-过氧-Cu配合物系统促进O-O -裂解的还原研究，特别是新的低自旋化合物，其中改变铜配体环境和血红素轴向“碱”配体是方法的一部分。系统地改变还原剂和酸将在研究中使用，以阐明对这一过程至关重要的因素，包括化学或生化系统中“氧活化”的关键方面，(3)具有铜配体咪唑-苯酚片段的配体系统的使用和研究，该配体系统可诱导相应血红素/铜- o2组装的O-O还原裂解化学。此外，将详细研究两种化学系统，以测试CcO（生物）化学如何导致铜配体His-Tyr交联的实际形成。(4)研究血红素轴向“碱”配体输入变化的化学系统，其中血红素/NO/O2配位化学将从机制上研究过氧亚硝酸盐的形成及其随后的反应性。这种化学反应发生在一氧化氮双加氧酶（NODs）中，这种酶对细胞一氧化氮稳态至关重要，并可能通过氨基酸硝化化学作用参与细胞信号传导。(5)研究

DESCRIPTION (provided by applicant): The long-term research objective is to design, synthesize and investigate model compound systems which can help elucidate fundamental aspects of structure, metal-ligation, spectroscopy and reactivity relevant to the dioxygen (O2) and nitrogen oxide (NOx) chemistry utilized by heme-copper oxidases (HCOs), nitric oxide reductases (NORs) and related proteins. HCOs and NOR's are evolutionarily related enzymes which play critical roles in cellular processes within aerobic and anaerobic organisms. They have in common a heme/M (M = Cu or non-heme Fe) active site that reductively cleaves O2 or NO, respectively. The research proposed will contribute to a better understanding of enzyme structure and mechanism by providing a comprehensive and fundamental basis relevant to biological processing of O2, NO and nitrite (NO2-), that extends even beyond the heme and Cu metalloprotein sphere. Specific aims include (1) the characterization of heme/Cu- O2 adducts, new protonated and low-spin derivatives and elucidation of their (structures) and electronic/bonding properties, (2) the study of reductive O-O cleavage promoted by heme-peroxo-Cu complex systems, especially new low-spin compounds where altering the copper-ligand environment and heme axial 'base' ligands is a part of the approach. Systematically varied reducing agents and acids will be employed in the investigations in order to elucidate those factors crucial for this process, comprising a critical aspect of 'oxygen activation' in chemical or biochemical systems, (3) the employment and study of ligand systems which possess a copper-ligand imidazole-phenol moiety which induces O-O reductive cleavage chemistry for a corresponding heme/copper-O2 assembly. Also, two chemical systems designed to test how CcO (bio)chemistry leads to the actual formation of the copper-ligand His-Tyr crosslink, will be studied in detail. (4) investigation of a chemical system with input variations f the heme axial 'base' ligand, where heme/NO/O2 coordination chemistry will be studied mechanistically with regard to peroxynitrite formation and its subsequent reactivity. This chemistry occurs in NO dioxygenases (NODs), enzymes critically involved in cellular NO homeostasis and possibly in cellular signaling via amino-acid nitration chemistry. (5) the study of chemistry relevant to NORs, heme/Cu assemblies that enable NO reductive coupling. A clear focus will be on the mechanism of formation of putative hypontrite intermediates, their structures and their reactivity leading to N2O and H2O products. Such information is key to the understanding of N-N coupling and N-O cleavage chemistries which are also coupled to protonation. These processes are also of broad interest with respect to other biological metalloenzyme nitrogen oxide processing. This aim also includes efforts to elucidate the chemistry of heme/Cu mediated nitrite reduction to NO and complementary NO oxidation to nitrite. In-hand heme/Cu assemblies enable this chemistry and further mechanistic probing is necessary; these processes are critical to NO signaling and linked to cellular responses to changes in [O2] concentrations.